Protein tyrosine kinase Syk is involved in Thy-1 signaling in rat basophilic leukemia cells.
Thy-1, a glycosyl-phosphatidylinositol-anchored surface glycoprotein, has been shown to possess transmembrane signaling capacity. In rat mast cells and rat basophilic leukemia cells (RBL) aggregation of surface Thy-1 with antibodies triggers a series of intracellular events, resembling those induced by aggregation of the high-affinity receptor for IgE (Fc epsilonRI), including tyrosine phosphorylation of multiple proteins and release of secretory components. Unlike the Fc epsilonRI-mediated activation, where both the membrane-associated protein tyrosine kinase (PTK) Lyn and the cytoplasmic PTK Syk are responsible for initiating the signaling cascade, only Lyn has been implicated in Thy-1-mediated activation in RBL cells. Here we report that Syk is also rapidly tyrosine phosphorylated upon Thy-1 cross-linking. Increased Syk tyrosine phosphorylation is observed only in cells in which extensive aggregation of Thy-1 is induced by two layers of cross-linking reagents. RBL-derived mutant cells deficient in the expression of surface Thy-1 and transfectants re-expressing surface Thy-1 were used to exclude the possibility that Syk activation reflects an interaction of the cross-linking reagents with surface molecules other than Thy-1. As Fc epsilonRI gamma subunits are well known to promote activation of Syk and its recruitment to membrane complexes, we also investigated the role of these subunits in Thy-1-mediated Syk activation, using RBL-derived mutant cells deficient in the expression of Fc epsilonRI gamma subunits and their revertants. Consistent with the lack of Fc epsilonRI expression, no IgE-induced response could be elicited, while Thy-1-inducible Syk phosphorylation was preserved. Our results suggest that Syk might be one of the kinases responsible for signal propagation upon Thy-1 cross-linking in a Fc epsilonRI-independent pathway.
Tolar
P
P
Department of Mammalian Gene Expression, Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Prague.
Dráberová
L
L
Dráber
P
P
D000818:Animals; D004792:Enzyme Precursors / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D007942:Leukemia, Experimental / Q000378:metabolism*; D008407:Mast Cells / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction; D000072377:Syk Kinase; D018800:Thy-1 Antigens / Q000378:metabolism*
D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D018800:Thy-1 Antigens; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606898:Syk protein, rat